Andy Murray's hopes of reaching the top will not be thwarted by a lack of fitness, according to the player's temporary coach Mark Petchey.

The teenager had cramp in his defeat to David Nalbandian at Wimbledon, again raising questions about his fitness.

"The top people push themselves through the pain barrier and Andy's going to have to do that if he wants to make it," Petchey told BBC Sport.

"The kid wants it too much to not go through that."

Petchey, who is the LTA men's training manager, added: "He just needs the right people to motivate him. We'll get him fit enough, I don't have any doubt about that.

"There are enough top fitness people in this country to make sure he's ok."

Murray, 18, also suffered from cramp when he lost to Thomas Johansson at Queen's last month.

And Petchey admits a lot of work needs to be done on the Scot's fitness.

"The cramping was partly dehydration and partly not being fit enough," Petchey said.

Maybe it will take a while for Andy to mix it week in week out with the best players

Mark Petchey

"You can see the quality of tennis is there as well as the mental attributes - now we've just got to get him fitter.

"There are no shortcuts and we'll find out about Andy's pain threshold very soon."

Some people have drawn unflattering comparisons between the fitness of Murray and another teenager - French Open champion Rafael Nadal.

But Petchey says this is unfair.

"Nadal is a year older. Sometimes it takes time to develop your game, it's not going to be an overnight success.

"It'll take a good 12, even 18 months to get it to where we need him to get it to.

"If this doesn't happen, then some serious questions will need to be asked why. If in two years' time Andy Murray isn't fit enough to go five sets, some questions will have to be asked, and quite rightly so."

Murray was out of action for six months last year after suffering a serious knee injury.

"His knee injury was pretty serious - there were question marks about whether it was a career-ending injury," Petchey said.

"You lose a bit of fitness after that and have to take it carefully. You can't go out pounding the roads.

"He's not that unfit. He's a junior coming here and there's a lot of nervous energy that's gone into what he's done. From my point of view he's handled it pretty amazingly.

"People have to be a bit realistic. Maybe it will take a while for Andy to mix it week in week out with the best players."